Erie , Pennsylvania -LRB- CNN -RRB- -- The image remains chilling nearly eight years later : a pizza deliveryman sitting cross-legged on the pavement with a homemade bomb clamped around his neck , surrounded by nervous police who crouch behind their cars .

`` Why is n't anybody trying to get this thing off me ? '' he shouts to the dozens of officers nearby .

But before a bomb squad can arrive , the device goes off , killing 46-year-old Brian Wells .

In the agonizing minutes before his death on August 28 , 2003 , Wells told police the bomb had been fastened to his body by people who ordered him to rob a bank and follow a detailed checklist before it would be disarmed -- instructions that amounted to a twisted scavenger hunt .

Timeline , evidence photos , video , 911 audio

The case fueled years of debate about whether the hapless Wells had been the victim of a heinous murder or a willing participant in a horrifically botched crime .

The FBI later concluded that Wells had been a participant and closed the books on the case in March . Two people that agents identified as having been part of the scheme are in prison ; a third has died .

But Wells ' family still believes he was a blameless victim -- `` innocent 100 percent , '' his sister , Jean Heid , told CNN .

`` They screwed up big time , '' Heid said . `` They let an innocent man , my brother , die while in their custody and they did n't even lift a finger to help him .

`` This case is going to be looked at for years to come , and they do n't want it known that they screwed up , '' she said . `` Brian never would have done this . ''

In particular , she said , one of the plotters escaped justice .

According to the FBI , Floyd Stockton knew of the robbery , but received immunity from prosecution and was allowed to go free . Prosecutors never called him as a witness in the trials , saying he was ill at the time .

The FBI believes a Stockton associate , William Rothstein , was the mastermind of the heist and likely made the bomb , the affidavit says . Bombmaking materials were found in Rothstein 's home .

According to the FBI affidavit , one of the admitted conspirators said Stockton carried the bomb out of Rothstein 's garage on the day of the robbery and handed it to Rothstein .

Read the entire FBI affidavit warrant

Rothstein then secured the bomb around Wells ' neck and followed him to the PNC Bank branch that Wells robbed shortly before his death , the affidavit states , quoting a witness who talked to Rothstein 's girlfriend , Marjorie Diehl-Armstrong .

Stockton is a registered sex offender who was a fugitive from a rape charge in Washington state at the time the plot unfolded and was staying with Rothstein at the time , according to court papers .

According to Kenneth Barnes , a convicted crack dealer who is now serving a 20-year prison term in the bomb plot , Stockton was to have divvied up the money from the bank heist .

Stockton has rebuffed repeated requests for comment from CNN , both by telephone and in person .

Barnes also gave the FBI information that implicated Wells . According to an FBI agent 's court affidavit , Barnes told authorities that Wells had been discussing the hold up about a month before it took place . Barnes ' story had been corroborated by another witness in the affidavit .

By all accounts , the 2003 case evolved into one of the most complicated and bizarre crimes in the annals of the FBI .

Police investigating fake collar bomb extortion plot

Half an hour before the bomb went off , Wells had walked into the PNC branch on Peach Street in Erie . The bomb sat on his chest beneath a white T-shirt , which had the word `` Guess '' spray-painted on it . And he carried a cane , which turned out to be a homemade shotgun .

Wells handed over a series of notes to the tellers , demanding $ 250,000 . Tellers did n't have nearly that much in cash , and Wells walked out with a little less than $ 9,000 .

Police caught up with him in the parking lot of a nearby eyeglass shop , where he died begging for help .

Because it was a bank robbery , the FBI became the lead investigative agency . Agents quickly assembled a task force of more than 50 law enforcement officers from a half-dozen federal , state and local agencies .

At first , the FBI saw Wells as a victim . Rich Schapiro , a writer for Wired magazine , has reported extensively on the case and told CNN that the notes Wells carried led him to believe he could live .

`` The note suggested at the very end of this , if he completed it in the allotted time -- which was n't much -- that he would be able to save his life , '' Schapiro said .

One federal law enforcement official says the cast of characters ultimately linked to the crime is `` like a band of criminal misfits . '' According to the FBI , those misfits began to turn on each other less than a month after Wells died .

On September 21 , Rothstein called Pennsylvania State Police to report that there was a body in his freezer -- the body of a man named James Roden , whom he said was killed because he was going to report the bomb plot to authorities , according to the FBI affidavit .

Rothstein told FBI agents that Roden had been killed by Diehl-Armstrong and that he had helped Diehl-Armstrong hide the body .

After her arrest , Diehl-Armstrong implicated Rothstein in the bomb plot , and she eventually told investigators she gunned down Roden when he threatened to go to police about the plan . Rothstein died of cancer before being officially linked to the crime .

Diehl-Armstrong is now serving prison terms both for the botched heist and for Roden 's killing . Her own lawyer says she has multiple personality disorders and sometimes has `` difficulty '' telling the truth .

` Pizza bomber ' conspirator gets life behind bars

Barnes , meanwhile , saw his 45-year sentence for the bomb plot reduced to 20 years because he cooperated with authorities .

And Stockton now lives in Bellingham , Washington , north of Seattle . He 's the one Wells ' sister wants brought to justice .

`` He did n't deserve immunity , `` Heid said . `` He 's the guilty one that killed my brother . He deserved to be brought to justice . ''

Prosecutors said Wells may have been duped into thinking the bomb was a fake before agreeing to take part in the holdup -- but they 're confident he was part of the plot from the beginning .

`` No one could have sat through this trial without understanding the degree of evidence linking Mr. Wells to these participants , '' Assistant U.S. Attorney Marshall Piccinini , who led the government 's case , told reporters .

And Jim Fisher , a retired FBI agent and writer , told CNN that he believes Wells was murdered as part of the plot .

`` It was a first-degree murder , '' Fisher said . `` This was an intentional , pre-meditated homicide . Moreover , it was extremely cruel in the way the crime was executed . ''

CNN 's Blake Luce and Curt Merrill contributed to this report .

@highlight

Case of bomb-wearing bank robber pizza delivery man occurred in 2003

@highlight

Man who allegedly knew about the bomb and the robbery was allowed to go free

@highlight

Erie , Pennsylvania , case one of the most bizarre bank robberies in FBI history

@highlight

Two people were convicted in the robbery ; FBI closed the case this year